Liquid crystal display elements have been widely employed as various display elements because of their low-voltage driving properties, low-energy consumption, and capability of reduction in size and thickness.
Most of the currently industrialized display elements are of TN (twisted nematic) made using nematic liquid crystals However, the TN display mode is slow in response in the order of few milliseconds, and it has recently turned out that a more rapid response can be obtained by using ferroelectric smectic liquid crystals.
Ferroelectric smectic liquid crystals are compounds typically exemplified by a 4-(4-n-decyloxybenzylideneamino)cinnamic acid 2-methylbutyl ester (hereinafter abbreviated as DOBAMBC), which was developed by R.B. Meyer, et al. in 1975, and are characterized by ferroelectric properties in their chiral smectic C phase as described in J. Physique. Vol. 36, L-63 (1975).
The liquid crystal thin film cell of DOBAMBC was found to exhibit a rapid response in the order of microsecond as described in N.A. Clark, et. al., Appl. Phys. Lett., Vol. 36, p. 899 (1980). With this as a momentum, the ferroelectric smectic liquid crystals have recently been attracting attention as materials promising for opto-electronics related elements, such as a photo printer head, a light Fourier transform element, and a light bulb, as well as display elements, such as a liquid crystal TV.
Since known ferroelectric liquid crystals, when used alone, find difficulty in obtaining a broad temperature range sufficient for practical use, they have been used as a blend of two or more thereof to broaden the temperature range in which a chiral smectic C phase is exhibited. Under the present situation, however, not only is limited the choice of ferroelectric liquid crystals themselves and compounding compounds which can be blended to that effect, but also the available blends of liquid crystals are still insufficient in performance for practical use.
On the other hand, the following compound is known as a phenyl ester of a phenyl nitrogen-containing hetero-aromatic carboxylic acid as disclosed in JP-A-62-149669 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). ##STR5## wherein Y represents an n-hexyl group, an n-octyl group, or an n-decyl group; and C* is an asymmetric carbon atom.
However, this compound has an extremely high temperature range for the chiral smectic C phase and is, therefore, difficult to apply to practical use.